The present nonprovisional application claims priority under 35 USC 119 to Japanese Patent Application No. 2001-394335 filed on Dec. 26, 2001 the entire contents thereof is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a two-wheel-drive/four-wheel-drive switching system for a vehicle.
2. Description of Background Art
Heretofore, a vehicle is known which can switch between two wheel drive and four wheel drive.
FIGS. 4 and 5 show an example of a vehicle for switching between two wheel drive and four wheel drive. The vehicle 1 is mainly composed of a body frame 3 in the center of which an engine 2 is mounted. Front wheels 4 and rear wheels 5 are arranged on both sides of the front and the rear of the body frame 3 with a steering handlebar 6 arranged on the upside of the front of the body frame 3 for steering the front wheels 4. A fuel tank 7 is attached to the body frame 3 and a seat 8 attached in the rear of the fuel tank 7.
A final reduction gear unit for the front wheel 13 and a final reduction gear unit for the rear wheel 14, respectively, are coupled to the engine 2 via propeller shafts 11 and 12 and are provided in the center of the front and the center of the rear of the body frame 3.
Drive shafts 9 are coupled to the right and the left of the final reduction gear unit 13 for the front wheels 4. The front wheels 4 are attached to the drive shafts 9 via wheel hubs 10 attached to the ends of the drive shafts.
Axle housings 22 into which drive shafts for the rear wheel 5 are inserted are provided to the right and the left of the final reduction gear unit for the rear wheel 14 and the rear wheels 5 are attached via wheel hubs 23 arranged at the ends of the axle housings 22 and coupled to the drive shafts.
A two-wheel-drive/four-wheel-drive switching system for switching a state of rear wheel drive and a state of four wheel drive by connecting or disconnecting power transmitted to the front wheels 4 is provided between the final reduction gear unit for the front wheel 13 and the propeller shaft 11, for example.
In the alternative, the two-wheel-drive/four-wheel-drive switching system may be also provided between the propeller shaft 12 in the rear and the final reduction gear unit for the rear wheel 14 to switch a sate of front wheel drive and a state of four wheel drive.
The states of drive are switched according to a state of a road and an operating state.
The two-wheel-drive/four-wheel-drive switching system is proposed in Japanese published unexamined patent applications No. Hei 11-1131 and No. Hei 10-297313, for example, and FIG. 7 shows the structure.
The two-wheel-drive/four-wheel-drive switching system 15 shown in FIG. 7 is shown by axially dividing an input shaft 16 of a final reduction gear unit for a front wheel 13 into two and is composed of two input shaft components 16a and 16b matched on the same axis and a switching unit 17 for connecting or disconnecting the shafts.
In more detail, a cylindrical positioning protrusion 18 protrudes from the center of the end face of the input shaft component 16a positioned on the side of the final reduction gear unit 13 for the front wheels 4. A positioning concave portion 19 is provided into which the positioning protrusion 18 is fitted so that the positioning protrusion can revolve. The positioning concave portion 19 is formed in the center of the end face of the input shaft component 16b and positioned outside. Both input shaft components 16a and 16b are positioned on the same axis by matching both input shaft components 16a and 16b so that the positioning protrusion 18 and the positioning concave portion 19 are fitted and are coupled so that they can revolve relatively easily.
Splines S1 and S2 are formed on the surfaces of the respective matched parts of both input shaft components 16a and 16b and the switching unit 17 is provided so that the switching unit surrounds the matched parts.
The switching unit 17 is composed of a slidable switching ring 20 on the inside face of which a spline is formed, which is fitted to the matched parts of both input shaft components 16a and 16b and the spline of which is engaged or disengaged with/from the respective splines S1 and S2. A driving mechanism 21 is provided for selectively moving the switching ring 20 in a position in which the switching ring 20 is slid in the axial direction of both input shaft components 16a and 16b and is engaged with only one input shaft component 16a or in a position in which the switching ring 20 is simultaneously engaged with the splines S1 and S2 of both input shaft components 16a and 16b. 
The two-wheel-drive/four-wheel-drive switching system 15 configured as described above turns into a state of two wheel drive in which only the rear wheels are driven by moving the switching ring 20 in one direction by the driving mechanism 21, engaging the switching ring with only one input shaft component 16a and disabling the transmission of driving force to the front wheels 4 and turns into a state of four wheel drive in which the switching ring 20 is engaged with the other input shaft component 16b by sliding the switching ring 20 in a state wherein the switching ring is engaged with one input shaft component 16a. Thus, driving force is transmitted to the front wheel 4 by coupling both input shaft components 16a and 16b and the front wheels 4 and the rear wheels 5 are simultaneously driven.
That is, as shown in FIG. 8, in a two wheel drive condition, the supply of driving current to the two-wheel-drive/four-wheel-drive switching system 15 is stopped and in a four wheel drive condition, driving current is continuously supplied.
In a four wheel drive condition, an indicator is illuminated so as to inform an operator that the current state of drive is four wheel drive. However, for a method of detecting a state of four wheel drive, a method may be provided of providing a detection switch that is turned on when the detection switch touches the switching ring 20 and a fork that moves the switching ring 20 while the switching ring 20 is moved to a position of four wheel drive and detecting that the detection switch is turned on.
Such a conventional type two-wheel-drive/four-wheel-drive switching system 15 has the following problem that needs to be improved.
That is, in case when the detection switch operated by the switching ring 20 and the fork is used to illuminate the indicator for showing a state of four wheel drive operation, an impact is applied to the detection switch and a noise may be produced every time a state of drive is switched.
The abrasion of the switch due to the impact has an effect upon the precision of the lighting of the indicator.
The invention is made in view of the problems of such a conventional type switch and the object of the present invention is to provide a two-wheel-drive/four-wheel drive switching system for a vehicle wherein noise is hardly made and a state of drive can be securely indicated.
A two-wheel-drive/four-wheel-drive switching system for a vehicle according to the present invention is provided with a switching unit provided to either of the power transmission mechanisms for connecting an engine and a front wheel via a final reduction gear unit and connecting the engine and a rear wheel via a final reduction gear unit for enabling or disabling the transmission of power in the power transmission mechanism. A control unit is provided that controls the drive of the switching unit and indication control means are provided that detects that the transmission of power in the power transmission mechanism wherein an indicator is illuminated so as to achieve the object of the invention. The indication control means detects a phase difference between the revolutions of a pair of final reduction gear units. When the phase difference is within a predetermined range, the indicator is illuminated.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.